Aircraft operate in flight under guidelines generally known as instrument flight rules (IFR) and visual flight rules (VFR). Under IFR travel, the pilot must file an IFR flight plan with air traffic control (ATC) and obtain an IFR clearance to fly a specified route and altitude to the destination airport. Continuous two-way radio communication between the aircraft and ATC is required. The flight plan information includes the departure airport, the destination airport, the route and altitude of flight, the estimated time of arrival, the amount of fuel on board, the number of passengers on board, type of aircraft and identification number, and phone numbers for persons to contact in emergencies.
IFR travel occurs in both radar and non-radar environments. In the radar environment, the position, air speed, and altitude of the aircraft are constantly updated to the air traffic controllers. The ATC tracks the aircraft on radar monitors. In an emergency, the pilot notifies ATC through radio voice communications and transponder signals. ATC continues to track the aircraft, and in the event it is downed, ATC has a reasonable estimate of its location on the ground, within a few miles. The accuracy of the location however is dependant on a number of factors. These factors include the altitude of the plane at the time radar contact is lost, the air speed of the aircraft, the distance to the radar facility, and the terrain.
In non-radar IFR environment, the air traffic controller depends on positioning reports given by the pilot at specific reporting points. The positioning report includes the time of arrival at the point, the altitude, and the estimated time of arrival at the next reporting point. The reporting points vary in distance apart, and may range from several miles to about one hundred thirty miles apart. In an emergency, the pilot notifies ATC as discussed above and provides his last known location. The location of the downed aircraft then can be estimated, but this estimate is generally less accurate than in a radar environment. Should the emergency prevent communication with ATC, the estimate may be even less accurate.
All IFR flight plans must be closed so that ATC knows that the aircraft has landed safely. When an IFR flight lands at a controlled airport, tower personnel automatically cancel the flight plan for the pilot. When an IFR flight lands at an uncontrolled airport, the pilot continues to have the responsibility to close the flight plan. The flight plan can be closed in flight if the aircraft can land during visual meteorological conditions. The cancellation can then be communicated to ATC by two-way radio. In instrument meteorological conditions, cancellation can only be made after the aircraft has landed. Physical limitations of VHF radio communications however can prevent the pilot from canceling the flight plan by radio. In that situation, the pilot is responsible for canceling the flight plan by telephone. Pursuant to ATC regulations, cancellation of an IFR flight plan must occur shortly after the estimated time of arrival. If this interval is exceeded, a search is begun, as discussed below. It may take several minutes to taxi, secure the aircraft and passengers, and locate a telephone. Until the flight plan is canceled the controlled airspace is restricted from use by other aircraft. ATC can not release the airspace for other landings or take-offs until the open flight plan is canceled. Prompt cancellation of the flight plan by the pilot allows other aircraft to use the airspace sooner.
As discussed above, meteorological conditions having appropriate distance visibility allow aircraft to fly under visual flight rules (VFR). Aircraft flying under visual flight rules are encouraged to file a flight plan, but are not required to do so. The flight plan information provides search and rescue protection for the pilot in the event of an emergency. The VFR flight plan must be closed within thirty minutes of the estimated time of arrival for the aircraft at the destination, or authorities will begin a search, as discussed below. In the event of an emergency, the location of the downed VFR aircraft can not be estimated with any high degree of accuracy. Estimates are made based on the flight plan data and take into account the range of the aircraft around the planned route.
The initial search is typically conducted by telephone. Personnel with the Federal Aviation Administration call the contact phone numbers listed in the flight plan to determine whether the aircraft has landed safely. If the pilot or aircraft is not located, an air and ground search begins for the possibly downed aircraft. Searches involve many persons, organizations, and additional aircraft. Search efforts are expensive and time-consuming. Air search efforts include flying the route stated in the flight plan and flying grids based on the last known location of the aircraft, its air speed, its direction of travel, and the wind speed and direction. A grid is a geographical area defined by longitudinal and latitudinal coordinates. It may take several hours or even days for a search to locate a downed aircraft. Weather conditions may prevent starting the air search immediately. In one known instance, an aircraft taking off from an airport went down approximately one and one-half miles from the runway in snowy weather. The plane was not located until almost four hours later.
To assist in the search and rescue of downed aircraft, all aircraft currently carry an emergency locator transmitter. The transmitter broadcasts a VHF signal which is traced by search and rescue aircraft using triangulation or homing procedures. The speed of the search depends on the accuracy of tracking the signal. Accuracy depends on several factors including the type of radio receiving equipment carried in the search aircraft, the geographic terrain of the area in which the aircraft went down, and the strength of the signal broadcast by the locator transmitter. The transmitter is battery powered, and the duration of transmission depends on the strength of the batteries. While the emergency locator transmitter has proved successful in assisting the location of downed aircraft, the various factors affecting accuracy tend to slow the search efforts. Also, the downed aircraft may have drifted off its planned flight route, so the search may be initiated many miles from where the aircraft is.
Accordingly, there is a need in the art for an apparatus and method of canceling aircraft flight plans and to improve the effectiveness of searches for downed aircraft.